Prior art ring debarkers utilize a multiplicity of debarking tools equally spaced around a hollow rotating rotor and adapted to forceably engage a log as the log moves through a central opening in the rotor. A tensioning means is provided to force the debarking tools into engagement with the log such that they will remove the bark from the log as the log moves through the rotating rotor. Entry of a log into the central opening of the rotor or hollow head causes the end of the log to contact the debarking tools. This contact of the log with the debarking tools forces the tools to an open or dilated position whereupon the ends of the tools will engage the outside of the log.
Prior art apparatus for pretensioning the debarking tools includes the use of a plurality of resilient neoprene bands. The bands are connected to the pivotal debarking tools and pretensioned so as to force the debarking tools inwardly toward the center of the opening of the rotor.
In one of the prior art arrangements the bands are pretensioned by a hydraulic system. Oil is introduced into hydraulic cylinders by way of a common manifold such that the hydraulic fluid pressure in each of the cylinders is equal. Accordingly, the tension generated in each of the bands is equal.
In another prior art arrangement a mechanical device is provided for pretensioning the neoprene bands. With this arrangement the force applied by the tools against the logs is dependent upon the character or characteristics of the individual bands.
A common problem with the prior art pretensioning mechanisms is the quantitative value of the tool tension applied by the tool against the surface of the log increases as the diameter of the log being debarked increases. This results in increased difficulty in opening the tools if large logs are fed into the debarking machine. Additionally, this increase in tool force applied by the tools against large logs is not required since the tools adequately debark smaller logs wherein a lesser force is applied by the debarking tools against the logs. The high tool force or tool tension generated by the tools against the larger logs frequently results in tool breakage, feed roll shaft breakage and bearing failure. Additionally, there can be a loss of fiber on larger diameter logs.
An additional problem occasioned by the construction of the prior art arrangements is presented with those machines having a hydraulic system for pretensioning the debarking tools. In such machines, in the event a knot passes under a tool, the tool must open further to ride over the protrusion. This opening action causes an increase in the hydraulic pressure in the pretensioning cylinder. Since all of the pretension cylinders are connected by a common manifold, the pressure in all the cylinders is increased. The effect of this is to contribute to the failure such as tool breakage, feed roll shaft breakage and bearing failure.
A further problem with these systems presents itself when a log with a significant sweep is placed in the machine. When the tools open to accommodate the periphery of a log having a curve or bend, the increased pressure in the pretension cylinders tends to move the tool center off the center line of the machine. This can also result in the failures referred to above and can also cause jamming of the machine and incomplete removal of bark from a log.
Another problem with the prior art debarking machines is that when the tools disengage the trailing end of the log, the tension force on the tools tends to cause the tools to close rapidly. The tools are caused to slam closed against a weldment which is equipped with a resilient neoprene facing or pad. Over a period of time this impact closing action can be detrimental to the tool mechanism particularly when the pad or facing breaks up or becomes separated from the weldment.
Attention is also directed to the Brundell et al. Pat. No. 2,785,715, issued Mar. 19, 1957; the Brundell et al. U.S. Pat. No. 2,857,945, issued Oct. 28, 1958; the Brundell et al. Pat. No. 2,903,028, issued Sept. 8, 1958; and the U.S. Brundell et al. U.S. Pat. No. 2,860,672, issued Nov. 18, 1958.
Attention is further directed to the Anderson U.S. Pat. No. 3,053,294, issued Sept. 11, 1962; the U.S. Bowers U.S. Pat. No. 3,709,272, issued Jan. 9, 1973; the U.S. Jonsson Pat. No. 3,973,607, issued Aug. 10, 1976; the U.S. Bush U.S. Pat. No. 3,587,684, issued June 28, 1971; and the Smith, et al. U.S. Pat. No. 4,122,877, issued Oct. 31, 1978.